To determine the residual chlorine in given water sample

To determine the residual chlorine in given water sample

Appartatus Required:  Beaker, Conical Flask

Reagents Required: Potassium Iodide, Acetic Acid, Sodium Thiosulphate, Starch

Theory: Residual chlorine is not found in natural (untreated) water while it comes in water after disinfecting it by the process of Chlorination.

Procedure: 

1. Take 25 ml water sample in flask.
2. Add a small crystal of Potassium Iodide & distilled water to make the sample 100 ml.
3. Add 10 ml acetic acid to act as buffer & to reduce the pH between 3.5 to 4.2.
4. After reaction, yellow colour would be generated.
5. Titrate above solution by N/40 Sodium Thiosulphate till yellow colour disappears.
6. Add 1 ml starch to produce blue colour.
7. Titrate above solution by N/40 Sodium Thiosulphate till blue colour disappears.
8. Note down the total titrant used. Let it be x ml.
9. Repeat the procedure with distilled water. Let it be y ml.

Calculation:

Residual Chlorine: (x-y) x 35.5 mg/l

Author : Unknown

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